INSKEEP: Fracking, I said fracking. The controversial process used to extract natural gas produces millions of gallons of wastewater. Now to cut costs, energy companies want to transport that leftover water on barges. But, the U.S. Coast Guard has concerns.

Katie Colaneri of member station WHYY reports.

KATIE COLANERI, BYLINE: Not all fracking wastewater is created equal. The ingredients include a high level of salts, heavy metals and some radioactive material. But the exact recipe tends to change from well to well and driller to driller.

That's why the Coast Guard wants to require ship owners test each load they carry to make sure it doesn't contain hazardous materials that aren't normally allowed to travel on the nation's rivers. But that could get complicated for the people who own the barges.

Peter Stephaich is CEO of Campbell Transportation in Pittsburgh. He says one barge could hold about 100 truckloads of wastewater from different drilling sites.

PETER STEPHAICH: One apple would spoil the bunch. And it would be very difficult for us to go back and find out whose water that was and undo that process.

COLANERI: Stephaich thinks the gas industry should be responsible for showing what's in it. But fracking wastewater is exempt from federal hazardous waste laws and doesn't have to be tested.

David Spigelmyer heads up the Marcellus Shale Coalition, a major industry trade group.

DAVID SPIGELMYER: Our industry does do thorough investigative analysis on a lot of the transportation loads that come onto area roadways.

COLANERI: Drillers in Pennsylvania's Marcellus Shale send a lot of that wastewater on trucks or rail cars to Ohio for disposal deep underground. Putting it on barges would be more cost effective, but under the Coast Guard's proposal, that would come with a price.